1. Field of Invention
The present invention relates to a liquid crystal device, such as a reflective liquid crystal device, a transflective liquid crystal device, or the like, using a passive-matrix, an active-matrix or a segmented driving system, and to electronic equipment using the liquid crystal device. Particularly, the present invention relates to a liquid crystal device which employs an internal reflection system including a reflecting electrode serving as a reflector or transflector which is provided on the side of a substrate which faces a liquid crystal, and to electronic equipment using the same.
2. Description of Related Art
A reflective liquid crystal device using external light, and not a light source, such as a back-light, or the like, for display is advantageous from the viewpoints of low power consumption, miniaturization, weight reduction, etc., and is conventionally used for portable electronic equipment, such as portable telephones, wristwatches, electronic notebooks, notebook-type personal computers, and the like, in which, particularly, portability is regarded as important. A conventional reflective liquid crystal device includes a transmissive liquid crystal panel composed of a liquid crystal held between a pair of substrates, a reflector attached to the back of the transmissive liquid crystal panel so that external light incident on the front side is reflected by the reflector through the transmissive liquid crystal panel, a polarizer, etc. However, this device has a long optical path from the liquid crystal isolated by the substrates to the reflector, and thus causes parallax in a display image, causing double display. The conventional reflective liquid crystal device is thus unsuitable for high-definition image display, and it is very difficult to display a high-quality image, particularly in color display, because colors are mixed in the above-described long optical path. Furthermore, since external light is attenuated during the time from incidence on the liquid crystal panel to reflection by the reflector, it is difficult for the liquid crystal device to perform bright display.
Therefore, a reflective liquid crystal device having an internal reflection system has recently been developed, in which a display electrode arranged on one of a pair of substrates, which is opposite to the external light incidence side, includes a reflector so as to bring the reflection position near the liquid crystal layer. As an example of such a liquid crystal device, Japanese Unexamined Patent Publication No. 8-114799 discloses a technique including forming pixel electrodes serving as reflectors on a substrate, laminating two films including a high-refractive index layer and a low-refractive index layer, or alternately laminating the films in layers, and forming an alignment layer thereon. In this technique, a multilayer film, including a high refractive index layer and a low refractive index layer, is provided on the reflectors to increase the reflectance of external light incident on the counter substrate side, thereby achieving a bright reflective display.
In the technical field of this type of liquid crystal device, under the general demand for increasing the quality of display images, and decreasing cost, it is very important to simplify the construction of the device and the manufacturing process while improving the brightness and definition of a displayed image.
However, in order to obtain high reflectance, the above-mentioned technique, in which the pixel electrodes also serve as reflectors, requires a multilayer film of at least two layers including a high refractive index layer and a low refractive index layer, which are provided on the pixel electrodes, and thus has the problem of complicating the multilayer film structure and, by extension, the construction and manufacturing process of the device.
The present invention has been achieved in consideration of the above problem and it is one aspect of the present invention to provide a reflective or transflective liquid crystal device which permits simplification of the construction and manufacturing process of the device, and which can display a high-quality bright image. The liquid crystal device may also be used in a plurality of electronic equipment.
In order to solve the above problem, a liquid crystal device of the present invention may include a first substrate, a transmissive second substrate provided to oppose the first substrate, a liquid crystal held between the first and second substrates, a reflecting electrode arranged on the side of the first substrate, which is opposite to the second substrate, a transmissive insulating film having a single-layer structure provided on the reflecting electrode d an alignment layer provided on the transmissive insulating film. The refractive index of the transmissive insulating film is set to a value lower than the refractive index of the liquid crystal and the refractive index of the alignment layer, and the width of the transmissive insulating film is set to be not less than a first predetermined width with which reflectance of a multilayer film including the reflecting electrode, the transmissive insulating film, and the alignment layer is at a maximum for blue light incident on the second substrate side, and not more than a second predetermined width with which reflectance of the multilayer film is at maximum for red light incident on the second substrate side. In the present invention, the refractive index of the liquid crystal is defined as the average of the extraordinary refractive index ne and the ordinary refractive index n0 of the liquid crystal.
In the liquid crystal device of the present invention, external light incident on the second substrate side is reflected by the multilayer film including the reflecting electrode, the transmissive insulating film, and the alignment layer, which are provided on the first substrate, through the transmissive second substrate and the liquid crystal, and is again emitted from the second substrate side through the liquid crystal and the second substrate. Therefore, for example, when a polarizer is arranged on the outer side of the second substrate, the strength of external light reflected by the reflecting electrode and emitted as display light through the liquid crystal can be controlled by controlling the alignment state of the liquid crystal using the reflecting electrode, i.e., an image can be displayed according to the image signal supplied to the reflecting electrode.
The external light reflectance of the multilayer film including the reflecting electrode, the transmissive insulating film, and the alignment layer provided on the first substrate adjacent to the liquid crystal is dependent on the wavelength and varies depending upon the refractive index of the transmissive insulating film. More specifically, it is found that with the refractive index of the transmissive insulating film lower than the refractive index of the liquid crystal and the reflective index of the alignment layer, the reflectance of the multilayer film for any of red light, blue light and green light, which together form white external light, is high. Therefore, in the present invention, the refractive index of the transmissive insulating film is set to be lower than the refractive index of the liquid crystal and the refractive index of the alignment layer.
The external light reflectance of the multilayer film including the reflecting electrode, the transmissive insulating film, and the alignment layer provided on the first substrate adjacent to the liquid crystal is dependent on the wavelength and varies depending upon the width of the transmissive insulating film. More specifically, it is found that the maximum reflectance occurs for blue light (i.e., electromagnetic waves at a wavelength of about 450 nm) with the transmissive insulating film having a relatively small width, and the maximum reflectance occurs for red light (i.e., electromagnetic waves at a wavelength of about 650 nm) with the transmissive insulating film having a relatively large width. It is also found that the maximum reflectance occurs for green light (i.e., electromagnetic waves at a wavelength of about 550 nm) with a width between the relatively small width with which the maximum reflectance occurs for blue light, and the relatively large width with which the maximum reflectance occurs for red light. Namely, the width of the transmissive insulating film with which the maximum reflectance is obtained increases in the order of blue light, green light and red light. Therefore, in order to increase the reflectance for three colors of light which form external white light, the width of the transmissive insulating film is preferably set to a width between the width (i.e., the first predetermined width) with which the maximum reflectance for blue light occurs, and the width (i.e., the second predetermined width) with which the maximum reflectance for red light occurs. Therefore, in the present invention, the width of the transmissive insulating film is set to be the first predetermined width or more, and the second predetermined width or less.
As a result, in the liquid crystal device of the present invention, external light is reflected to the inside of the first substrate (i.e., the side adjacent to the liquid crystal), decreasing parallax in a display image by an amount corresponding to a decrease in length of the optical path, and improving the brightness of the display image as compared with a conventional reflective liquid crystal device in which external light is reflected by a reflector provided on the outer side of the first substrate. This permits a high resolution bright display, and a high resolution color display. Particularly, in order to achieve a high resolution bright reflective display, the reflecting electrode is formed on the first substrate, and the transmissive insulating film having a single-layer structure is formed on the reflecting electrode, thereby simplifying the structure of the multilayer on the first substrate, the whole construction of the device, and the manufacturing process of the device as compared with the above-described conventional technique of alternately laminating a high refractive index film and a low refractive index film on the pixel electrodes serving as reflectors.
Therefore, the prevent invention can realize a liquid crystal device which enables simplification of the construction and manufacturing process of the device, and high-quality bright image display.
In the liquid crystal device in accordance with one aspect of the present invention, the width of the transmissive insulating film is set to a value close to the third predetermined width which is between the first and second predetermined width, rather than the first and second predetermined widthes, with which the reflectance is at a maximum for green light incident on the second substrate side by the multilayer film.
In this aspect, since the width of the transmissive insulating film is set to a value between the first and second predetermined widthes, and near the third predetermined width with which the reflectance is at a maximum for green light incident on the second substrate side by the multilayer film, particularly, the green light for which spectral luminous efficacy is maximum, can be efficiently reflected to display a visually bright image.
In another aspect of the liquid crystal device of the present invention, the refractive index of the transmissive insulating film is 1.5 or less, and the width of the transmissive insulating film is 50 nm to 100 nm.
In this aspect, in order to obtain high reflectance, the transmissive insulating film having a single-layer structure having a refractive index of 1.5 or less and a width of 50 to 100 nm is formed on the reflecting electrode, thereby simplifying the manufacturing process of the multilayer film formed on the first substrate, for obtaining high reflectance.
In a still another aspect of the liquid crystal device of the present invention, the transmissive insulating film includes silicon oxide as a main component.
In this aspect, the transmissive insulating film including silicon oxide as a main component is formed on the reflecting electrode to obtain high reflectance, thereby obtaining high reflectance by a relatively easy manufacturing process at relatively low cost.
In a further aspect of the liquid crystal device of the present invention, the transmissive insulating film contains inorganic oxide particles having an average particle size of 50 nm or less.
In this aspect, the transmissive insulating film contains inorganic oxide particles having an average particle size of 50 nm or less to improve adhesion to the alignment layer formed on the transmissive insulating film, thereby relatively easily manufacturing the liquid crystal device, and improving reliability of the device.
In a still further aspect of the liquid crystal device of the present invention, the reflecting electrode includes aluminum as a main component.
In this aspect, the reflecting electrode including aluminum as a main component is formed on the first substrate to obtain high reflectance, thereby obtaining high reflectance by a relatively easy manufacturing process at relatively low cost.
In a further aspect of the liquid crystal device of the present invention, the reflecting electrode includes a plurality of stripe reflecting electrodes made of a conductive reflecting film, and a plurality of stripe transmissive electrodes made of a conductive transmissive film are further provided on the second substrate so as to cross the stripe reflecting electrodes.
In this aspect, the liquid crystal device is a so-called passive-matrix-driving-system reflective or transflective liquid crystal device in which an electric field is successively applied to the liquid crystal portions at the intersections of the plurality of stripe reflective electrodes on the first substrate and the plurality of stripe transmissive electrodes on the second substrate between the reflecting electrodes and the transmissive electrodes to control the alignment state of each of the liquid crystal portions, thereby controlling the strength of external light reflected by the reflecting electrodes and emitted as display light through each of the liquid crystal portions.
In a further aspect of the liquid crystal device of the present invention, the reflecting electrodes include a plurality of pixel electrodes arranged in a matrix and made of a conductive reflecting film, a two-terminal switching element connected to each of the pixel electrodes is provided on the first substrate, and one of a plurality of scanning lines and a plurality of data lines connected to the two-terminal switching elements is provided on the first substrate, and the other one of the plurality of scanning lines and the plurality of data lines is provided on the second substrate so as to cross the one of the plurality of scanning lines and the plurality of data lines on the first substrate.
In this aspect, the liquid crystal device is a so-called active-matrix-driving-system reflective or transflective liquid crystal device including the two-terminal switching elements, such as TFDs (Thin Film Diode), wherein an electric field is successively applied to the liquid crystal portions of the pixel electrodes between the pixel electrodes on the first substrate and the data lines or scanning lines on the second substrate to control the alignment state of each of the liquid crystal portions, thereby controlling the strength of external light reflected by each of the pixel electrodes and emitted as display light through each of the liquid crystal portions. Particularly, since electric power is supplied to each of the pixel electrodes through the switching element, such as the TFD, or the like, cross-talk between the respective pixel electrodes is decreased, and display of a high-quality image can be achieved.
In the liquid crystal device in a further aspect of the present invention, the reflecting electrodes include a plurality of pixel electrodes arranged in a matrix and made of a conductive reflecting film, and a three-terminal switching element connected to each of the pixel electrodes and a plurality of scanning lines and a plurality of data lines connected to the three-terminal switching elements are further provided on the first substrate.
In this aspect, the liquid crystal device is a so-called active-matrix-driving-system reflective or transflective liquid crystal device including the three-terminal switching elements, such as TFTs (Thin Film Transistor), wherein an electric field is successively applied to the liquid crystal portions of the pixel electrodes on the first substrate to control the alignment state of each of the liquid crystal portions, thereby controlling the strength of external light reflected by each of the pixel electrodes and emitted as display light through each of the liquid crystal portions. Particularly, since electric power is supplied to each of the pixel electrodes through the three-terminal switching element, such as the TFT, or the like, cross-talk between the respective pixel electrodes is decreased, and display of a high-quality image can be achieved. Counter electrodes made of a conductive transmissive film may be further provided on the second substrate opposite to the pixel electrodes so that the liquid crystal portion of each of the pixel electrodes is driven by a vertical electric field perpendicular to the first substrate, or the liquid crystal portion may be driven by a lateral electric field parallel to the first substrate without the counter electrodes.
In order to solve the above problem, electronic equipment of the present invention includes the above-described liquid crystal device of the present invention.
Therefore, in accordance with the electronic equipment of the present invention including the liquid crystal device of the present invention, it is possible to simplify the construction of the device and the manufacturing process thereof, and realize various electronic equipment, such as a portable telephone, a wristwatch, an electronic notebook, a notebook-type personal computer, etc., which are capable of displaying high-quality images.
The operations and other advantages of the present invention will be made clear from the embodiments described below.